Hackers stole 339.5 million rubles ($6 million) in an attack on the SWIFT international payments system in Russia last year, the Russian Central Bank said on February 16.

Quoted by TASS, the bank said it had been sent information about “one successful attack on the workplace of a SWIFT system operator,” resulting in the money being stolen.

A spokeswoman for SWIFT, whose system is used daily to transfer trillions of dollars, declined to comment on the case.

SWIFT noted late last year that digital heists were on the rise as hackers use increasingly sophisticated methods.

In December, hackers tried to steal 55 million rubles ($974,600) from Russian state bank Globex using the SWIFT system, and digital thieves made off with $81 million from the Bangladesh Bank in February 2016.